Waterborne disease outbreaks and increased cases of gastrointestinal illness have raised questions about the adequacy of distribution system barriers. The expansive nature of the distribution system makes it vulnerable to contamination. In particular, pressure transients-i.e., surges or water hammer-offer opportunities for intrusion of contaminants from the external environment. This study set out to determine the occurrence of indicator microorganisms and pathogens in the vicinity of potable water pipelines and assess the potential for intrusion created by transient distribution system pressure changes. Soil and water samples were collected immediately exterior to drinking water pipelines at eight locations in six states. Samples were tested for the occurrence of total and fecal coliforms, Clostridium perfringens, Bacillus subtilis, coliphage, and enteric viruses. Indicator microorganisms and enteric viruses were detected in more than half of the samples examined. Utilities need to be aware of the potential for water quality degradation to occur during pressure transients. Study results emphasize the need to maintain an effective disinfectant residual in all parts of the distribution system and to reduce leakage to minimize the potential for microbial intrusion into potable water supplies. In addition, research should focus on gaining insight into the role of pressure transients on drinking water quality, including development of techniques to evaluate system vulnerability to negative pressure and use of microbial or other indicators to predict pathogen intrusion into the distribution system.
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